bpo-44635: Convert None to NoneType in the union type constructor (GH-27136)

Author: serhiy-storchaka

Diff for: Lib/test/test_types.py

@@ -612,6 +612,8 @@ def test_or_types_operator(self):
         self.assertEqual(str | int, typing.Union[int, str])
         self.assertEqual(int | None, typing.Union[int, None])
         self.assertEqual(None | int, typing.Union[int, None])
+        self.assertEqual(int | type(None), int | None)
+        self.assertEqual(type(None) | int, None | int)
         self.assertEqual(int | str | list, typing.Union[int, str, list])
         self.assertEqual(int | (str | list), typing.Union[int, str, list])
         self.assertEqual(str | (int | list), typing.Union[int, str, list])
@@ -699,6 +701,13 @@ def test_or_type_operator_with_TypeVar(self):
         assert TV | str == typing.Union[TV, str]
         assert str | TV == typing.Union[str, TV]
 
+    def test_union_args(self):
+        self.assertEqual((int | str).__args__, (int, str))
+        self.assertEqual(((int | str) | list).__args__, (int, str, list))
+        self.assertEqual((int | (str | list)).__args__, (int, str, list))
+        self.assertEqual((int | None).__args__, (int, type(None)))
+        self.assertEqual((int | type(None)).__args__, (int, type(None)))
+
     def test_union_parameter_chaining(self):
         T = typing.TypeVar("T")
         S = typing.TypeVar("S")
@@ -754,7 +763,11 @@ def test_or_type_operator_with_SpecialForm(self):
         assert typing.Union[int, bool] | str == typing.Union[int, bool, str]
 
     def test_or_type_repr(self):
+        assert repr(int | str) == "int | str"
+        assert repr((int | str) | list) == "int | str | list"
+        assert repr(int | (str | list)) == "int | str | list"
         assert repr(int | None) == "int | None"
+        assert repr(int | type(None)) == "int | None"
         assert repr(int | typing.GenericAlias(list, int)) == "int | list[int]"
 
     def test_or_type_operator_with_genericalias(self):

Diff for: Misc/NEWS.d/next/Core and Builtins/2021-07-14-13-54-07.bpo-44635.7ZMAdB.rst

@@ -0,0 +1 @@
+Convert ``None`` to ``type(None)`` in the union type constructor.

Diff for: Objects/unionobject.c

@@ -67,9 +67,6 @@ union_instancecheck(PyObject *self, PyObject *instance)
     }
     for (Py_ssize_t iarg = 0; iarg < nargs; iarg++) {
         PyObject *arg = PyTuple_GET_ITEM(alias->args, iarg);
-        if (arg == Py_None) {
-            arg = (PyObject *)&_PyNone_Type;
-        }
         if (PyType_Check(arg)) {
             int res = PyObject_IsInstance(instance, arg);
             if (res < 0) {
@@ -99,9 +96,6 @@ union_subclasscheck(PyObject *self, PyObject *instance)
     Py_ssize_t nargs = PyTuple_GET_SIZE(alias->args);
     for (Py_ssize_t iarg = 0; iarg < nargs; iarg++) {
         PyObject *arg = PyTuple_GET_ITEM(alias->args, iarg);
-        if (arg == Py_None) {
-            arg = (PyObject *)&_PyNone_Type;
-        }
         if (PyType_Check(arg)) {
             int res = PyObject_IsSubclass(instance, arg);
             if (res < 0) {
@@ -175,9 +169,6 @@ union_richcompare(PyObject *a, PyObject *b, int op)
         Py_ssize_t b_arg_length = PyTuple_GET_SIZE(b_args);
         for (Py_ssize_t i = 0; i < b_arg_length; i++) {
             PyObject* arg = PyTuple_GET_ITEM(b_args, i);
-            if (arg == (PyObject *)&_PyNone_Type) {
-                arg = Py_None;
-            }
             if (PySet_Add(b_set, arg) == -1) {
                 Py_DECREF(b_args);
                 goto exit;
@@ -239,6 +230,9 @@ flatten_args(PyObject* args)
                 pos++;
             }
         } else {
+            if (arg == Py_None) {
+                arg = (PyObject *)&_PyNone_Type;
+            }
             Py_INCREF(arg);
             PyTuple_SET_ITEM(flattened_args, pos, arg);
             pos++;
@@ -365,6 +359,10 @@ union_repr_item(_PyUnicodeWriter *writer, PyObject *p)
     PyObject *r = NULL;
     int err;
 
+    if (p == (PyObject *)&_PyNone_Type) {
+        return _PyUnicodeWriter_WriteASCIIString(writer, "None", 4);
+    }
+
     if (_PyObject_LookupAttrId(p, &PyId___origin__, &tmp) < 0) {
         goto exit;
     }